On Tue, 19 Jan 1999, Gayle Callis wrote:

> Interesting comment about deterioration of plus charge slides.
>
> I just talked to my Erie Scientific rep, and he said the opposite about
> silanized slides, that they get better with age, but gave no scientific
> basis for that statement, any comments?  I have always dated
> poly l lysine slides, since this is a protein, and tried to use them
> within 6 months.

   Both types work by imparting a positive charge to the surface of
   the glass. With silanized slides, amino groups are covalently
   joined to the polymeric SiO2 molecular units of which glass is
   made. Polylysine (there is no reason to use poly-L-lysine;
   poly-DL-lysine is a bit cheaper, though both are expensive) is
   a large molecule bristling with amino groups. Except in
   strongly alkaline conditions, these amino groups are protonated
   (positively charged). This allows them to attract the predominantly
   negative charge of structural proteins of animal tissues. It also
   sticks polylysine to the negatively charged (silicic acid) surface
   of glass.

   These charge attractions are easily changed by the
   ambient pH. For silanized slides or polylysine, adhesion to the
   "typical" proteinaceous section will be least effective in an
   alkaline medium. Cartilage is different because its matrix is
   full of sulphate-ester groups, which are strong acids - negative
   at any pH. Cartilage can therefore be expected to adhere more
   securely to a positively charged surface than most other tissues.

   Chrome-gelatin is an old-fashioned but excellent adhesive that
   works by forming strong coordinate bonds with oxygen atoms of
   carboxyl groups, which are present in all proteins and in many
   lipids and carbohydrates. It works well in alkaline conditions,
   but fails if strong acids are used - as in some antigen retrieval
   procedures.

> However, the newer lot seems to be the problem.  Thanks to the manufacturers
> who put those invaluable lot numbers on products, at least they can see
> if others are cplaining/having problems.
> Beginning to think gremlins live in buffers.

    It's easy to believe something could go wrong in silanizing a
    huge number of slides. I do my own, by hand, and have had one
    bad batch of 100 (it was the first attempted) in 3 years. They
    were bad only for a pretty severe test that involved heating in
    an alkaline solution. Chrome-gelatin was somewhat better.

   Commercial silanized slides seem to be a bit better than those
   we make in the lab, but they are frightfully expensive.
   The commercial silanized slides don't come with a prescription
   for making you own. I suspect that instead of the regular
   published technique they use a reagent that covalently binds
   a quarternary nitrogen (positive charge at any pH) to the glass.
   Our local silicon chemist says this should be better, and has
   advised me about potentially better silanizing compounds.
   Some of these will soon be tested ....

    Rather a long comment on a sensible answer to a significant
    question!  If you've bothered to read it to the end, then,
    Thanks. Please let me know if you disagree, and why.  Email
    has reintroduced the noble tradition of the Letter as a form
    of discourse (our 4 bears would have said "intercourse")
    among scientists. It's unfortunate that the writing and mailing
    of real letters on paper are now too costly for frequent use,
    unless you're sending an advert or a bill.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1